Serving various programs by broadcasting them repeatedly, each new broadcast beginning when the preceding has ended does not satisfy users. On the other hand serving the selected video program on a separate channel to each user upon request is expensive and inefficient.
For satisfying a user's request for a video program without too much delay, an approach known as Near-Video-On-Demand (N-VOD) has been developed, wherein each video program is repeatedly made available at a fixed staggered time interval, thereby reducing the maximum delay to the staggered time interval, which is typically several minutes.
An improvement strongly reducing the maximum time delay between the user's request and the availability of the video program is known as Hybrid-Video-On-Demand (HVOD). A description of that approach is given in U.S. Pat. No. 5,682,597 to which reference may be made. According to that approach, multiple copies of each program are continuously sent on separate channels and again the start of each copy is offset by a staggered time interval. At the user's end, VOD requests which are not synchronous with the beginning of a transmission are initially fulfilled with the start of a specific additional transmission of the beginning portion of the selected video program for that user, while simultaneously maintaining use of the NVOD transmission for that requestor. The in-progress transmission of the selected video program is stored in a buffer associated with the viewbox and spliced to a conclusion of the beginning portion of the video program for output by the viewbox and display.
That approach requires specific transmission of the beginning portion of the selected video program on request by only one user and still increases the amount of network resources which are required. Network resources can be saved by providing a large size buffer in the viewbox and storing the beginning portion of each of the video programs once for each period during which the programs remain unchanged (once a week for instance). Then there is no need to transmit the beginning portion of a selected program to the respective user. The volume of data to be transmitted is reduced and downloading of the beginning portions may take place when the network load is low. A user's request for an in-progress program is initially and immediately fulfilled by reading the beginning portion from the buffer while the remaining portion is stored for later read-out after splicing. A buffer allowing simultaneous read-out and writing is necessary, since storage proceeds after splicing.
A limiting factor in the implementation of that approach is the buffer size. Typically transmissions of all video or multimedia programs on the network start at the same time For any selected program to be immediately available to a user even in the worst conditions, when the request takes place just before a new transmission of the N programs takes place, the buffer capacity required for storing the beginning portions is little less than N times the staggered time interval. A shorter staggered time interval and conversely a greater number of simultaneous time offset transmissions of a same program require a lesser buffer size but increasingly draw on network resources.